The study of the mechanistic and synthetic aspects of cationic olefin cyclizations will be continued. The mechanisms of cyclization of conformation-ally mobile cyclohexyl systems will be established in order to determine the reasons for the differences in stereochemistry of cyclization from cases which are not conformationally mobile. The synthetic utility of olefinic cyclizations for synthesis of erimophilane sesquiterpenoids will be examined. The applicability to total synthesis of trichothecane sesquiterpenoids of electrocyclic reactions of cationic intermediates will be examined in further detail.